1. Field of the Invention
The invention is based on a method for operating a drive train with an electrical machine, and on an apparatus for performing the method.
2. Description of the Prior Art
Exhaust gas posttreatment systems, such as the Diesel particle filter (DPF) or the NOx-storing catalytic converter (NSC), are used to maintain exhaust gas limit values. In the case of the Diesel particle filter, the particles that occur in combustion are collected. At high exhaust gas temperatures, the collected particles are burned off, and the Diesel particle filter is evacuated again. However, this is done only at high load, without additional interventions. Moreover, provisions for increasing the temperature, such as purposefully lessening the engine efficiency by shifting injection to late, postinjection, and so forth, or preheating the intake air and regeneration of the Diesel particle filter, can be possible over a wider operating range. However, the result is fewer advantages of the Diesel engine over the Otto engine. It can also happen that if the load and rpm are too low, regeneration of the Diesel particle filter is not possible, because of the low exhaust gas temperature. This range presents a problem for the operating reliability of the Diesel particle filter.
The operation of the NOx-storing catalytic converter is subdivided into NOx storage phases and regeneration phases. Because of the limited storage capacity of the NOx-storing catalytic converter, these phases alternate in rapid succession. In the NOx-storing catalytic converter, the NOx storage efficiency is poor at low exhaust gas temperatures. Particularly in the first phase of the so-called New European Driving Cycle, this leads to comparatively high NOx emissions. The regeneration of the NOx-storing catalytic converter is done in the rich mode at an air number λ<1, since uncombusted hydrocarbons are needed to reduce the stored NOx molecules. For attaining the rich mode, the engine is choked, and the injection is adjusted such that at the same engine moment, a greater mass of fuel is injected. This in turn means markedly lower efficiency during the regeneration, and hence a lessening of the advantages in terms of fuel consumption over the Otto engine.
From German Patent Disclosure DE 101 60 018 A1, a drive with an internal combustion engine and an electrical machine has been disclosed, in which as a function of an instantaneous demand for power to the drive and as a function of the instantaneously available power of the drive, an optimal engine rpm is predetermined by means of coordinated triggering of the engine and the electrical machine, while maintaining the instantaneous power demand.